In a project at the Wisconsin Center for Space Automation and Robotics (WCSAR), it was attempted to employ porous stainless steel tubes through which an aqueous nutrient solution was moved by capillary action into the larger pores of an artificial rooting medium. The tubes were buried in the artificial rooting medium and the larger pores of the medium remained substantially filled with air. Pressure sensors and flow meters monitored the controlled operation. The capillary movement of water into and out of the rooting medium was demonstrated. See "21st Century Gardener", Vol. 3, No. 2, pp. 43-48 (May 1989).
In a related project (same citation), the ability to humidify or dehumidify air in a temperature and pressure regulated chamber was evaluated using a single porous tube through which water was circulated. The temperature of the circulating water in the tube was manually regulated to adjust the temperature of the tube wall relative to the dew point temperature of the air in the chamber. Above the dew point, water evaporated through the tube walls while, below the dew point, moisture condensed from the chamber air on the exterior surfaces of the tube and moved into the tube through the tube walls. The capacity to change the humidity of the chamber air was demonstrated.
The apparatus and methods used in those projects were suitable only for showing the general feasibility of using a porous tube wall as a water or water vapor transport medium. Practical apparatus and methods are necessary to permit actual usage of a porous tube for humidification and dehumidification.
The present invention is directed to such practical apparatus and methods.